The environmental impacts of sulphur dioxide released during flood basalt eruptions may be more limited than previously thought, reports a paper published online this week in Nature Geoscience.

Sulphur dioxide has been shown to lead to climatic cooling and acidification of the environment, including ‘acid rain’. During a flood basalt eruption, up to several million cubic kilometres of lava are released over a period of several hundred thousand years, along with volcanic gases such as sulphur dioxide. Many flood basalt eruptions coincide with mass extinction events, which has led to the suggestion that massive sulphur dioxide release may have contributed to the Cretaceous-Paleogene and end-Permian mass extinctions. However, recent research suggests that flood basalt eruptions-and hence sulphur dioxide release-could be intermittent, characterized by years to decades of activity followed by periods of inactivity.

Anja Schmidt and colleagues use numerical models to simulate the environmental impacts of such an intermittent sulphur dioxide release during two eruptions-the Deccan Traps in India (65 million years ago), and the Roza eruption (14.5-16.5 million years ago) that created the Columbia River basalts in the northwestern United States. They find that, although acidic sulphur-based compounds were deposited to soils and freshwater systems, most regions away from the eruption site were resistant to acidification and lasting damage. Furthermore, the climate recovered from cooling caused by the sulphur dioxide release within 50 years of the eruption ceasing. The authors conclude that only individual eruptions lasting centuries or more would have had widespread and lasting environmental impacts. They argue it is therefore unlikely that acidification from sulphur dioxide released during flood basalt eruptions contributed substantially to global-scale mass extinction.